1. Field of the Invention
The present invention generally relates to multi-piece golf balls having a solid core and cover. Particularly, the ball contains an inner core (center) made of a foamed composition and surrounding outer core layer. The inner core is preferably molded from a polyurethane foam material and the outer core is preferably formed from polybutadiene rubber. The outer surface of the inner core preferably has a non-uniform structure and includes projecting members. A single or multi-layered cover may be disposed about the core structure.
2. Brief Review of the Related Art
Multi-piece, solid golf balls having a solid inner core protected by a cover are used today by recreational and professional golfers. The golf balls may have single-layered or multi-layered cores. Normally, the core layers are made of a highly resilient natural or synthetic rubber material such as styrene butadiene, polybutadiene, polyisoprene, or highly neutralized ethylene acid copolymers (HNPs). The covers may be single or multi-layered and made of a durable material such as HNPs, polyamides, polyesters, polyurethanes, and polyureas. Manufacturers of golf balls use different ball constructions (for example, three-piece, four-piece, and five-piece balls) to impart specific properties and features to the balls.
The core is the primary source of resiliency for the golf ball and is often referred to as the “engine” of the ball. The resiliency or coefficient of restitution (“COR”) of a golf ball (or golf ball component, particularly a core) means the ratio of a ball's rebound velocity to its initial incoming velocity when the ball is fired out of an air cannon into a rigid plate. The COR for a golf ball is written as a decimal value between zero and one. A golf ball may have different COR values at different initial velocities. The United States Golf Association (USGA) sets limits on the initial velocity of the ball so one objective of golf ball manufacturers is to maximize the COR under these conditions. Balls (or cores) with a high rebound velocity have a relatively high COR value. Such golf balls rebound faster, retain more total energy when struck with a club, and have longer flight distances as opposed to balls with lower COR values. Ball resiliency and COR properties are particularly important for long distance shots. For example, balls having high resiliency and COR values tend to travel a far distance when struck by a driver club from a tee. The spin rate of the ball also is an important property. Balls having a relatively high spin rate are particularly desirable for relatively short distance shots made with irons and wedge clubs. Professional and highly skilled recreational golfers can place a back-spin on such balls more easily. By placing the right amount of spin and touch on the ball, the golfer has better control over shot accuracy and placement. This is particularly important for approach shots near the green and helps improve scoring performance.
Over the years, golf ball manufacturers have looked at adjusting the density or specific gravity among the multiple layers of the golf ball to control its spin rate. In general, the total weight of a golf ball needs to conform to weight limits set by the United States Golf Association (“USGA”). Although the total weight of the golf ball is mandated, the distribution of weight within the ball can vary. Redistributing the weight or mass of the golf ball either towards the center of the ball or towards the outer surface of the ball changes its flight and spin properties.
For example, the weight can be shifted towards the center of the ball to increase the spin rate of the ball as described in Yamada, U.S. Pat. No. 4,625,964. In the '964 patent, the core composition preferably contains 100 parts by weight of polybutadiene rubber; 10 to 50 parts by weight of zinc acrylate or zinc methacrylate; 10 to 150 parts by weight of zinc oxide; and 1 to 5 parts by weight of peroxide as a cross-linking or curing agent. The inner core has a specific gravity of at least 1.50 in order to make the spin rate of the ball comparable to wound balls. The ball further includes a cover and intermediate layer disposed between the core and cover, wherein the intermediate layer has a lower specific gravity than the core.
Chikaraishi et al., U.S. Pat. No. 5,048,838 discloses a three-piece golf ball containing a two-piece solid core and a cover. The inner core has a diameter in the range of 15-25 mm, a weight of 2-14 grams, a specific gravity of 1.2 to 4.0, and a hardness of 55-80 JISC. The specific gravity of the outer core layer is less than the specific gravity of the inner core by 0.1 to 3.0, less than the specific gravity of the inner core. The inner and outer core layers are formed from rubber compositions.
Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece ball with a dense inner core made of steel, lead, brass, zinc, copper, and a filled elastomer, wherein the core has a specific gravity of at least 1.25. The inner core is encapsulated by a lower density syntactic foam composition, and the core construction is encapsulated by an ionomer cover.
Multi-layered balls containing inner cores made of relatively low-density compositions such as foam also are described in the patent literature. For example, Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ball containing a core comprising an inner and outer portion, and a cover made of a material such as balata rubber or ethylene acid copolymer ionomer. The core is made by foaming, injecting a compressible material, gasses, blowing agents, or gas-containing microspheres into polybutadiene or other core material. According to the '889 patent, polyurethane compositions may be used. The compressible material, for example, gas-containing compressible cells may be dispersed in a limited part of the core so that the portion containing the compressible material has a specific gravity of greater than 1.00. Alternatively, the compressible material may be dispersed throughout the entire core. In one embodiment, the core comprises an inner and outer portion. In another embodiment, the core comprises inner and outer layers.
Sullivan and Binette, U.S. Pat. No. 5,833,553 discloses a golf ball having core with a coefficient of restitution of at least 0.650 and a cover with a thickness of at least 3.6 mm (0.142 inches) and a Shore D hardness of at least 60. According to the '553 patent, the combination of a soft core with a thick, hard cover results in a ball having better distance. The '553 patent discloses that the core may be formed from a uniform composition or may be a dual or multi-layer core, and it may be foamed or unfoamed. Polybutadiene rubber, natural rubber, metallocene catalyzed polyolefins, and polyurethanes are described as being suitable materials for making the core.
Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf ball containing a low specific gravity core and an optional intermediate layer. This sub-assembly is encased within a high specific gravity cover with Shore D hardness in the range of about 40 to about 80. The core is preferably made from a highly neutralized thermoplastic polymer such as ethylene acid copolymer which has been foamed. The cover preferably has high specific gravity fillers dispersed therein.
Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball comprising: i) a pressurized foamed inner center formed from a thermoset material, a thermoplastic material, or combinations thereof, a blowing agent and a cross-linking agent and, ii) an outer core layer formed from a second thermoset material, a thermoplastic material, or combinations thereof. Additionally, a barrier resin or film can be applied over the outer core layer to reduce the diffusion of the internal gas and pressure from the nucleus (center and outer core layer). Preferred polymers for the barrier layer have low permeability such as Saran® film (poly(vinylidene chloride), Barex® resin (acyrlonitrile-co-methyl acrylate), poly(vinyl alcohol), and PET film (polyethylene terephthalate). The '294 patent does not disclose core layers having different hardness gradients.
Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654 discloses a golf ball having a foamed intermediate layer. Referring to FIG. 1 in the '654 patent, the golf ball includes a core (12), an intermediate layer (14) made of a highly neutralized polymer having a reduced specific gravity (less than 0.95), and a cover (16). According to the '654 patent, the intermediate layer can be an outer core, a mantle layer, or an inner cover. The reduction in specific gravity of the intermediate layer is caused by foaming the composition of the layer and this reduction can be as high as 30%. The '654 patent discloses that other foamed compositions such as foamed polyurethanes and polyureas may be used to form the intermediate layer.
Tutmark, U.S. Pat. No. 8,272,971 is directed to golf balls containing an element that reduces the distance of the ball's flight path. In one embodiment, the ball includes a core and cover. A cavity is formed between core and cover and this may be filled by a foamed polyurethane “middle layer” in order to dampen the ball's flight properties. The foam of the middle layer is relatively light in weight; and the core is relatively heavy and dense. According to the '971 patent, when a golfer strikes the ball with a club, the foam in the middle layer actuates and compresses, thereby absorbing much of the impact from the impact of the ball.
Although some conventional multi-layered core constructions are generally effective in providing high resiliency golf balls, there is a continuing need for improved core constructions in golf balls. Particularly, it would be desirable to have multi-layered core constructions with selective specific gravities and mass densities to provide the ball with good flight distance along with spin control. It further would be desirable to develop core structures, wherein the inner core is made of a low-density material such as a foam composition. The present invention provides core constructions and golf balls having such properties as well as other advantageous features and benefits.